(1) Field of the Invention
The present invention relates to an expansion valve for cooling recycling systems for use in vehicles and the like, more particularly to an expansion valve having an actuator for imparting an additive force to the spring of the expansion valve.
(2) Description of the Prior Art
A conventional expansion valve of this kind is disclosed, for instance, in Japanese Utility Model Lying-Open Specification No. 175272/1983. FIG. 1 shows the expansion valve.
The expansion valve 1 comprises mainly a pressure chamber 2, an expansion chamber 3 and a valve body 4 consisting of a valve rod 11, a valve 12, and a spring 13. A coolant is sealed in the pressure chamber 2 and its pressure is varied. This variation is caused by temperature changes detected by a detecting rod member or a temperature/pressure converter 5 mounted at the outlet of an evaporator 22 of a cooling recycling system 21 shown in FIG. 2. The diaphragm 6 of the expansion valve 1 is operated upwards or downwards, that is, the diaphragm 6 is pushed in the upward or downward direction due to the change in pressure in the chamber 2 in accordance with the temperature detected.
The expansion chamber 3 is provided with an orifice 10 adapted to communicate with an opening 9 which in turn communicates with a primary path 7 to be connected to a compressor 23 as shown in FIG. 2, with a secondary path 8 to be connected to an evaporator 22 also shown in FIG. 2. In FIG. 2, reference numeral 24 indicates a condensor and numeral 25 indicates a liquid tank or reservoir.
The valve body 4 including the valve rod 11, the valve member 12, and the spring 13 is provided within the expansion chamber 3. One extreme end of the valve rod 11 is connected to the diaphragm 6 in the pressure chamber 2, while the other end of the rod 11 is connected to the valve member 12. The valve member 12 is supported by the upper end of the spring 13 which is in turn fixed at the bottom of the expansion chamber 3 in order to control the opening of the orifice 10 and to normally bias the valve member 12 in the direction of the arrow A in FIG. 1 to close the orifice 10.
The opening of the orifice 10 is normally adjusted at a predetermined position, that is, the closed position when the sum of the pressure of the spring 13 and the pressure in the expansion chamber 3, and the pressure in the pressure chamber 2 are balanced, and the orifice 10 is opened when the valve member 12 is moved in a opposite direction to the arrow A in FIG. 1, in accordance with the change in pressure within the pressure chamber 2. Namely, the valve rod 11 is moved downwards in accordance with the movement of the diaphragm 6 which expands in the downward direction in accordance with the pressure change in the pressure chamber 2. As a result, the valve member 12, one end of which is connected to the valve rod 11, is shifted in a direction opposite to the arrow A, against the force of the spring 13.
Accordingly, the valve member 12 cannot be opened unless a pressure larger than the pressure sum of the force of the spring 13 and the pressure in the expansion chamber 3 is applied to the upper portion of the pressure chamber 2 of the diaphragm 6. As a result, a coolant overheat condition called "superheat" is determined by the force of the spring 13 initially set up.
As described above, since the superheat is determined by the bias force of the spring 13 of the expansion valve 1 according to the prior art, the amount of the superheat tended to be normally constant.
Now, the result of experiments by the applicant shows that the superheat may be 15 degrees at the beginning of the start of cooling, while in a stable condition it may decrease to 5 degrees, as shown in FIG. 3. However, since the superheat cannot be selected to only one amount or one value in view of the relationship with the set-up value of the spring 13 as described above, the value of the stable condition of 5 degrees is normally selected. Accordingly, since the performance of the superheat in the early starting period of the operation was sacrificed, the development of an expansion valve has long been desired in which the superheat can be changed in accordance with every change in the temperature of the evaporator 22 by detecting its temperature.